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Bugrowave Window Fan

Pest-free nighttime air
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Like many regions (you limeys don't know how well you've got it), my locale is home to a wide variety of blood-sucking flying insects, from the stealthy black fly, who has bitten you and scarpered off before you know she's been there, to the less subtle but persistent and agile mosquito, all the way up to the dreaded moosefly, who operates with all the subtlety of a sledgehammer to the groin but will sit there and chew on your arm for as long as he pleases while calmly weathering a fusillade of direct hits from a large-caliber handgun (which I must now resort to since my wife has imposed a general moratorium on the use of flamethrowers inside the house).

**yes, yes, [Alterother], that's very humorous and exaggerational, but is there any actual partial confectionary involved here?** Okay, sorry, I've been into the tomatoes and I'm feeling a bit verbose.

My most-loved enemy of the entemological world, however, is the lowly gnat; too small to bothered by conventional window screens, able to wiggle through all but the finest of mosquito netting, and appearing in nightly swarms to assault me en masse whilst I'm tucked up with a good book. They seem to prefer me, actually; my wife, whom I beleive has been bitten (by gnats) once or twice, takes evil delight in insisting that they don't exist.

So here's the bisected biscuit:

A window fan that draws air through a short duct, focused upon the center of which is an ultra-low-yield magnetron. It doesn't have to be big enough to cook your jacket potato, nor even to boil a teaspoon of water--just enough to splode their little buggy brains as they sallie through intent on miniature nocturnal exsanguination of yours truly. The duct is baffled so the microwaves don't slow-cook the canary, and a clean-out chute provides nutritional garnish for my breakfast cereal. Now I am no longer pestered by tiny stinging insects and can better focus on my beloved evening pastimes of reading and blasting away at mooseflies with my .45. (Yes, we have screens; I let the mooseflies in on purpose, for entertainment value)

Alterother, Jun 14 2011

Microwave Oven http://en.wikipedia...ave_oven#Principles
Crude, yet effective. [8th of 7, Jun 14 2011]

Visible patterns in microwave oven http://www.youtube....ure=player_embedded
Using Xmas balls ? Looks more like neon bulbs (NE-2) [csea, Jun 15 2011, last modified Jun 16 2011]

Reticulated scrambled eggs Reticulated_20scrambled_20eggs
Heating patterns in microwave [lurch, Jun 16 2011]

(??) Insect Heating http://ddr.nal.usda...7/1/IND20548389.pdf
Insects can be microwaved [MechE, Jun 23 2011]

(?) Microwave Kiln http://www.microwav...ln-Fuseworks/Detail
[Klaatu, Feb 25 2013]

[link]






       Small insects are not heated or killed by microwaves. A mosquito will fly around in an active microwave oven, quite happily.
spidermother, Jun 14 2011
  

       Oh, well, bugger that for a lark, then. What is it, a mass issue?   

       So, let's come up with an alternative method of slaughter. Maybe something involving hydrogen, perhaps?
Alterother, Jun 14 2011
  

       Seriously, I actually did approximately 3 seconds of research on this one, and nobody mentioned that. What use is the internet if there's no valid info available regarding the effects of microwaves on small pestiferous insects?
Alterother, Jun 14 2011
  

       The invention of the laser mosquito zapper makes this redundant.
marklar, Jun 14 2011
  

       That's been invented, has it? Does it work on gnats? Does it cost less than my car?
Alterother, Jun 14 2011
  

       Approximately 3 seconds research with a microwave oven would have been more informative.
spidermother, Jun 14 2011
  

       Well put.
Alterother, Jun 14 2011
  

       It might work with a weaponized magnetron firing an intense beam.
rcarty, Jun 14 2011
  

       Even if it wouldn't work, it was still fun to write. Bonus points for wasting the time of whoever bothered to read it.   

       [rcarty] love the enthusiasm, but re: non-canary-killing. My wife is rather fond of da boids.
Alterother, Jun 14 2011
  

       Microwaves should work on insects, their blood (ichor?) is still water based, and enough heat will take them out.
MechE, Jun 14 2011
  

       Fish and Game regulations vary from state to state, but the .45 may be overkill - consult your local authorities.
normzone, Jun 14 2011
  

       Anything much smaller than the wavelength of the radiation is not affected by it. If you don't want to test this on an insect, place a small drop of water on a saucer. Place it in a microwave oven, alongside a glass partly filled with water (to avoid damaging radiation levels within the oven). The water in the glass gets hot, while the small drop stays quite cool.   

       The cutoff size is around 1 cm; for instance, small (individual) sultana grapes are not heated, while very large grapes are. A very big moth would probably explode, but a small one won't. (I tried this with a smallish moth, many years ago; it was completely unaffected. That's how I know).
spidermother, Jun 14 2011
  

       Sounds like someone has done extensive research on this one.   

       A scanning IR laser would appear to be the best solution.
8th of 7, Jun 14 2011
  

       Someone has two microwave ovens at home, a (mostly) science/plasma one, and a (mostly) food one. As stated elsewhere, someone should probably get a life.   

       //IR laser// That'd do it. Shine the laser into an IR reflective (e.g. polished aluminium) cavity, for simplicity.
spidermother, Jun 14 2011
  

       [Spider] I'd like to see documentation on that. It might make sense if a microwave used standing waves, but it seems unlikely. Microwaves act on individual molecules, not on bodies as a unit.
MechE, Jun 14 2011
  

       // someone should probably get a life //   

       Good idea - go Google for that on the WWW.   

       // if a microwave used standing waves //   

       Ah, but they do.   

       If you conduct microwave energy into an enclosure (i.e. an oven) then a stable pattern of nodes and antinodes will develop <pedant> almost </pedant> instantly.   

       Microwave ovens rely on either a "stirrer" ( rotating slotted baffle) or a turntable to ensure that the contents (note: not necessarily edible) get evenly heated.   

       For 2.45 gigahertz, the wavelength is 122 millimetres, more than sufficient for those pesky little bugs to slip through the gaps, damn them.   

       // blasting away at mooseflies with my .45 //   

       Fair amount of skill and accuracy needed there ... a Mossberg 12-guage firing 3-inch magnum, No.9 shot, is more effective as a swatter. But indoors, make sure you wear hearing protection, until you're outdoors - takes typically between four and five shots.   

       <later>   

       It occurs to us that a mesh small enough to provide a reasonable amount of microwave attenuation into the dwelling is going to keep out a fiar number of bugs, too ...
8th of 7, Jun 14 2011
  

       From the annotations, it is indisputable that a significant number of HalfBakers have practical experience of placing non-food items (and indeed living creatures, albeit mere arthropods) in microwave ovens, and gratuitiously blasting them with RF energy just to see what happens.   

       Well done, chaps. Carry on.
8th of 7, Jun 14 2011
  

       Further research: It's not the size, as such, that matters, it's that the interference at the walls produces plenty of dead spots larger than the insect for it to land in (flying/elevated insects do get fried). Combined with the low cross section and thus low incident radiation which gives them time to find an area where they aren't being baked alive, they can survive.   

       A properly designed bugrowave would prevent this by having a uniform, high power field in the area the insects can travel through.   

       In practical terms, however, a bugzapper type screen would probably be cheaper and easier to build.
MechE, Jun 14 2011
  

       What you need here is simple vortex-separation, the same technology we use to keep dust and sand out of military engines operating in dusty environments. Spin the buggers in a fast-enough mini-cyclone, they won't escape.
RayfordSteele, Jun 14 2011
  

       Use the mesh as a susceptor.
lurch, Jun 14 2011
  

       itty-bitty railgun.
FlyingToaster, Jun 14 2011
  

       Photon torpedoes (NB Fish and Game regulations vary from state to state).
8th of 7, Jun 14 2011
  

       All mimsy were the Bugrowaves...
csea, Jun 14 2011
  

       //tucked up with a good book. They seem to prefer me,// Maybe it's your choice of reaing matter. Try swapping books with your wife, one night, and see who gets bit.
mouseposture, Jun 14 2011
  

       It's really very much simpler to keep a small herd of bats? (Herd of bats?? Of course you have.)   

       "More rapid than eagles his flittermice came,
And he whistled, and shouted, and call'd them by name:
"Now, Gnatter! Now, Mother! Now, Sonar, and Echo!
"On Foxface, on Horseshoe! Remove that mosquito!"
MaxwellBuchanan, Jun 14 2011
  

       Eat less salty and potassium-filled foods and they'll be more attracted to someone else.
RayfordSteele, Jun 15 2011
  

       Dammit, I suspect it true about the standing waves, and short of a moving wave reflector it's not going to improve anytime soon.   

       What you could do is plot the waves and where two intersect, put a plastic guide tube for the midgey to fly through en route to it's dinner appointment.   

       Although just having two magnetrons a fair distance apart, with the beams crossing would do the trick and you cheer up birds on a winter's day be thawing the ice on your neighbour's bird bath from across the street...
not_morrison_rm, Jun 15 2011
  

       [nmr] (Obligatory) Don't cross the beams!   

       //Microwaves act on individual molecules, not on bodies as a unit.// That's not true. It's a myth that's been around at least since microwave ovens started getting popular. Microwaves heat in a way not fundamentally different from the way infrared heats (although on a larger scale, corresponding to the longer wavelength).   

       //Further research: It's not the size, as such, that matters, it's that the interference at the walls produces plenty of dead spots larger than the insect for it to land in (flying/elevated insects do get fried).// Incorrect. It's the size, as such.   

       //Combined with the low cross section and thus low incident radiation// Incorrect. What about the cube/square law? That would mean that small insects fry quicker, not slower.   

       which gives them time to find an area where they aren't being baked alive, they can survive.// Incorrect. Have you ever seen an ant running in circles on the turntable so that it stays in the same (safe) spot? Or a small grape?
spidermother, Jun 15 2011
  

       [FT] Once again, we think alike; in lieu of recent threads, I figured I'd probably be baked alive if I proposed a miniaturized PHALANX system.   

       [mouse] There's no way I'm reading a single word of Vampire Academy. Hard as it may be to believe, I still have a shred of dignity.   

       I love it when I initiate really intense scientific discussions amongst people who know way, way more than I do about this stuff. It makes me feel comfortably unimportant by comparison.
Alterother, Jun 15 2011
  

       //Photon torpedoes// Gamma rays?
TomP, Jun 15 2011
  

       // Microwaves heat in a way not fundamentally different from the way infrared heats (although on a larger scale, corresponding to the longer wavelength).//   

       Not true. Microwaves heat through di-electric heating, not radiative. The misconception is that they heat "from the center out" instead of heating only to skin depth (which will be deeper if it has a relatively dry outer skin).   

       //What about the cube/square law? That would mean that small insects fry quicker, not slower.//   

       Cube square law works in my favor as well. Volume goes up as the cube, surface area goes up as the square.   

       Since heat loss is on the surface area, and microwave absorption is based on volume (for object thickness less than the skin depth) a small insect re-radiates more of the total heat it absorbs than a larger object.   

       //Incorrect. Have you ever seen an ant running in circles on the turntable so that it stays in the same (safe) spot? Or a small grape?//   

       Not having actually studied the microwave patterns inside a microwave, I suspect that most of the quarter inch or so near the walls/floor is fairly dead, so little running around is required, but the insect will move if its in a hot spot.   

       Try putting that grape on a pedestal (inverted glass?) and see what happens.
MechE, Jun 15 2011
  

       /my wife, whom I beleive has been bitten (by gnats) once or twice, takes evil delight in insisting that they don't exist./   

       Maybe they do not, and it is scabies or perhaps young fleas residing in your easy chair?
bungston, Jun 15 2011
  

       See [link] for clever means of observing microwave patterns within a (specially modified) oven.   

       A comment below the video talks about an even simpler technique: place thermal paper on the oven floor, and see where it darkens.
csea, Jun 15 2011
  

       Pondering the wonders of microwaves, it would be interesting to put a flat paper with some thermally sensitive paint stuff in the microwave, to see if the waves generate a pattern.
bungston, Jun 15 2011
  

       An easier way is to lay out a tray of marshmallows and see which ones melt, I've seen it done.
mitxela, Jun 15 2011
  

       [bungston] Oh, sure, my chair is _full_ of fleas. But the gnats get me in bed. They fly over her to get to me. Seriously.
Alterother, Jun 16 2011
  

       I'm still right, dammit.   

       I just tried another experiment. I put a dead bee on the end of a bamboo skewer, which I placed in a small medicine glass, so the bee was about 4'' above the oven's floor, along with a glass of water. Result: no detectable heating of the bee.   

       In case my dead bee was too dry, I dipped it in water and immediately repeated the experiment. The bee was soaking wet and had a drop of water clinging to it. Result: the water in the glass boiled, but the bee was still cold - not even slightly warm.   

       There is no way this could be explained by cooling of the bee due to its greater surface area to volume ratio. If the bee's water and that in the glass were receiving the same mass-specific heating flux then the bee would have become noticeably hot.
spidermother, Jun 23 2011
  

       <applause>
8th of 7, Jun 23 2011
  

       <bows>
spidermother, Jun 23 2011
  

       I trust the above experimants were properly documented and are now available to the general public?   

       This is what the internet is for!
Twizz, Jun 23 2011
  

       My annos here are all the documentation you're getting, for now. They're repeatable, and fun, experiments, and I simply encourage others to try them.   

       For completeness, I also tried a shallow plastic lid, about 3'' across, filled to a depth of a few mm with water. As expected, it boiled faster than the water in the glass. Here, high surface area to volume works in favour of rapid heating.   

       The general explanation is that objects have to be of the order of the wavelength of the radiation, or larger, to absorb significant energy. They also must have intermediate conductivity; very good conductors and very good insulators absorb very little energy. Those rules allow good prediction of the behaviour of objects in microwave ovens; for instance, incandescent light globes light up, big lumps of metal and cold glass remain cold, but red-hot glass gets hotter, and melts, as hot glass is slightly electrically conductive. Microwaves are fun!   

       (Conductivity might be an oversimplification; the explanation for the heating of non-conducting but polar substances, such as pure water, is that the molecules partly align themselves with the changing electric field; the result is equivalent to a very tiny oscillating current, where the charges are constrained to movements smaller than the size of a water molecule. Nevertheless, the heating effect is a bulk property of the water, and does not act on individual molecules as such. I suppose you could model the water as a resistance and a capacitance in series.)
spidermother, Jun 23 2011
  

       //astounding// I agree. I didn't quite believe it until I tried it. You can heat part of an ordinary glass jar to red heat on a gas stove, quickly transfer it to a microwave oven, and blast it on high. It takes a while, and can't be too good for the magnetron, but it keeps glowing, and slowly sags and pools.
spidermother, Jun 23 2011
  

       So what absorbs the microwaves in the light bulb case? The (very thin) metal base, the even thinner filament, the non-conductive glass, or the vacuum inside the bulb. No individual component is anywhere near the wavelength (or even .1 of the wavelength) required for absorption by your statement.   

       I'm willing to ackowledge that something unusual is happening, but I still question wether it was the size of the object.
MechE, Jun 23 2011
  

       See link for information on the use of microwaves to kill grain pest insects inside the grain without excessive heating of the host material. Note that most of the studies referenced are at a lower frequency (longer wavelength) than commercial microwave ovens.
MechE, Jun 23 2011
  

       It's the entire conductive part, including the filament and the wires that support the filament, which is typically 2-3 cm in extent. That the partly resistive component - the filament - is relatively short does not matter. Because it is in the middle, it is able to dissipate energy as alternating current is induced in the entire conductive length.   

       An object only needs to be large in a single dimension. A single strand of fine steel wool, laid out straight, turns white hot in an instant. According to my theory, a tiny ball of steel wool should not heat up much.   

       (30 seconds later) Yep, tested and confirmed. A screwed up ball of steel wool about the size of a large match head does absolutely nothing, while a few strands teased out to a length of about 2'' instantly vapourises.   

       One more hypothesis, relevant to the light bulb. A large nail should not get hot, but if two nails are placed end to end, with a tiny gap bridged by steel wool, the steel wool should get hot (even if it is too small to be affected on its own). Here goes...   

       ... Again, exactly as predicted. I even used the exact same little ball of steel wool that was unaffected on its own. When placed between the nails, it melted and sparked. A nail on its own remained cold.   

       The next obvious experiment is to zap a long, narrow trough of water. It should get hot, even if it's only a few mm wide, as long as it is a couple of cm or more long.   

       ... Confirmed. This was relatively easy; just a few ml of water in a rectangular take-away container, propped up at one end so a narrow channel formed in the other.   

       Your linked article is interesting; however, insects in a bulk substance, such as flour or grain, are different from an insect in isolation. A bunch of grapes, or a cup of rice, is heated by microwaves, whereas individual (small) grapes or rice grains are not. Likewise, an insect embedded in rice should be heated; the rice+insect as a whole acts as a sufficiently large object.
spidermother, Jun 23 2011
  

       I'll take your word for it, but I still don't think size is the driving factor in this.   

       In fact, the article I link to suggest that insects have relatively low absorption in the microwave range, but have a much higher absortpion in the RF range, which has considerably longer wavelengths. If size were the driving factor, the reverse would be true.
MechE, Jun 23 2011
  

       Interesting. I've yet to read the article in detail; it does say, though, that for the longer wavelengths, the exposure is more uniform - which suggests lower attenuation rates, and lower absorbances.   

       It's also worth noting that in all cases, the medium (wheat or flour) was significantly heated; the article mentions the desired but unattained goal of heating the insect to lethal temperatures while the medium stays sufficiently cool. That also points to bulk effects.
spidermother, Jun 23 2011
  

       the goal can and should be accomplished, but microwaves are not the way. Instead, you want the air to pass through a countercurrent flow device with a heater at the apex, such that cool air enters, warms up to roast the bugs at the apex, then gives back almost all of that energy to the incoming fresh air. The exhaust temperature will be as close as you want to the inlet temperature, without any living bugs in it.
ReBuildIt, Feb 25 2013
  

       I still think it's possible to use microwaves, indirectly, to kill the little critters. Have the fan push them through a microwave kiln. <link> It is hot enough to fuse glass, and should toast gnats and no-see-ums to crunchy perfection.
Klaatu, Feb 25 2013
  
      
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